Encrypt local databases

[manuroe]

We have to replace None in the code with a secret.

We should manage this secret like on EI where we have a protocol and different implementations to manage secrets.

[manuroe]

The key management must be compatible with ElementR-iOS. EIX needs to be able decrypt and use the crypto DB used in EIR.

[pixlwave]

We're going to wait to implement this until the SQLite support is available for the state store in the SDK.

[manuroe]

Let's try it on nightlies first.